Setting offsets by timestamp fails without the topic name option

[ognjen-j]

When using set offsets for a certain timestamp, the command fails if no topic name is provided (-t option). Since everything works correctly when using an absolute value as an offset, the error is presumably caused by the part of the function that fetches the closest offsets for the given timestamp.
If the topic name is omitted, esque should assume all topics for which the consumer has offsets (the same way it already does with absolute offset values).